I love reading threads when, "in pops" the a**hole- know-it-all, with all the answers on how... "things that are different are "bad"..... (I'm going to play that guy now.)
Engine oil contains HC (hydrocarbon). If you store your firearms in a cool room, or area where there is high humidity or condensation, H2O will combine with the HC, which equalls Hydrochloric Acid. Gun oils have a completely different design and purpose than engine oil.
You may say "what happens inside an engine with "engine-oil". Well, this is why ALL engine oil companies recommend not idleing your engine, where the engine temperature is too low to burn off any condensation. Also, oil change intervals are recommended well before the actual life-span of the oil is due. In heavy truck applications, ALL manufactures state that the engine, if needed to idle, be set on high idle above 1000 rpm. This ensures that the engine temp is high enough to deplete any condensation, and eliminate the possibility of Hydrochloric acid forming.
Yep and the above post is a prime example.
Ummmm, What do you think ALL oils are made of? Do you know what a hydrocarbon really is? Do you realize that (almost) everything that burns has carbon in it? And everything that burns has hydrogen in it, and every oil has hydrogen in it?
All oils/fats have carbon except silicone oils, which substitute a silicon atom for the carbon atoms, and even then there are still some carbon atoms attached to it.
Where do you think the water and acid come from???? Hint =>, maybe from the FUEL!!! What do you get when you burn a hydrocarbon? Ummm, CO2 and WATER VAPOUR (the hydrogen atoms from the hydrocarbon chain have to go, be turned into something)
As for the acids? To get hydrochloric acid you need a CHLORINE source, typically from chloride, ie, various salts. In an engine, it is primarily sulphuric acid, from SULPHUR in the fuel. So do you run your gun on high sulphur gas or diesel?



Back on topic,
As for oils on guns, there are no parts on a gun where lubrication is critical. Yes there are high loading on some parts, but not when the parts are sliding. It is not like an engine that has bearings that are continuously stressed and sliding pistons that run through maybe 150,000 cycles PER HOUR. More wear than the majority of guns will get in several lifetimes.
So basically use whatever works. I use synthetic engine oil.